method and device for production of wrapping pipes for a bundle of hollow fibres

Abstract: A wrapping pipe for a bundle of hollow fibers comprises a plastic sheet (S) welded at its opposing edges by ultrasonics and having no difference in level of the inner surface.

Description: The present invention relates to a method and a device for the production of wrapping pipes for a bundle of hollow fibers and, more particularly, a method and a device for the production a tubular of member for protecting a bundle of hollow fibers from breakage or contamination until the bundle of the hollow fibers is loaded into a housing or a cylindrical container of blood treatment devices used for hemodialysis, hemofiltration, hemodiafiltration or the like. When applying hollow fibers to blood treatment devices such as dialyzer, it is custom to protect hollow fibers from damages or contaminations until a bundle of the hollow fibers are loaded into a cylindrical container of the blood treatment device. The protection of hollow fibers has been carried out with a satin finished sheet or an extruded pipe of plastics. For example, the hollow fibers are protected by winding the plastic sheet round a bundle of hollow fibers and fixing an overlapped portion of the plastic sheet with several pieces of an adhesive tape as illustrated in Fig. 5, or by loading a bundle of hollow fibers into an extruded plastic pipe as shown in Fig. 6. However, such protective members have some problems awaiting a solution. For example, the use of the plastic sheet is troublesome to handle. In addition, when winding the plastic sheet round the bundle of hollow fibers, the outermost hollow fibers of the bundle are frequently damaged as they are caught in an overlapping portion between the inner and outer ends of the sheet, causing leakage of the blood during blood treatment. Further, the hollow fibers caught in the overlapping portion of the sheet are folded down when loading into the cylindrical container, causing blockade or folds of the hollow fibers. Thus, it is required to replace the damaged hollow fibers with new ones to avoid leakage of the blood. Another troubles are that some sheets wound round the hollow fibers are turned down at the comer of its outer end and that some wrapped articles of the hollow fibers get a flat configuration. In such cases, the wrapped articles are occasionally caught in a conveying device during automatic transportation, resulting in discontinuation of the wrapping operation. Some of the above problems caused in the use of the sheet are solved by use of the extruded pipe. However, it is impossible with the current extrusion molding techniques to produce extruded pipes with a satin finished inner surface. Since the extruded pipe has a mirror finished inner surface, the coefficient of friction between the pipe and hollow fibers is large when pulling out the hollow fibers from the extruded protective pipe to load them into the cylindrical container for the blood treatment device, resulting in damages due to bends of the hollow fibers. Thus, it is required to replace the damaged hollow fibers with new ones. A method and device for producing wrapping pipes is known from CH-A-462 445. It is therefore an object of the present invention to provide a method and a device for production of wrapping pipes for hollow fibers. Such wrapping pipes are to prevent the hollow fibers from being caught in the sheet or folded down when loading them into the wrapping pipe or taking out of the pipe, as well as from being caught in a conveying device during automatic transportation. According to the present invention, a wrapping pipe can be produced by a device comprising: a pair of rollers for drawing a plastic sheet from a plastic sheet roll; a sheet cutting station including a pair of cutters for cutting the sheet drawn by said rollers to a predetermined width; a cylindrical core rod for rounding the sheet into a tubular form having an overlapped portion at opposing longitudinal sides thereof; a mold movably arranged around said core rod for shaping the rounded sheet into a tubular form, said mold having a through hole and a slit extending in the longitudinal direction of the mold, an ultrasonic welding means including a welding horn for welding the overlapped portion of the sheet by ultrasonic waves, said welding horn being movably arranged above the slit so that it is insertable into the slit to press the overlapped portion of the sheet against the core rod to form a continuing pipe having an inner surface with no difference in level of the inner surface thereof; and a pipe cutting station including a cutting member for cutting the continuing pipe into a pipe with a predetermined length. The aformentioned device produces a wrapping pipe for a bundle of hollow fibers, consisting of a plastic sheet in the form of a hollow cylinder, said sheet being welded at longitudinal opposing sides thereof by ultrasonics and having no difference in level of an inner surface thereon. Preferably, the wrapping pipe has an inner surface with a center line mean roughness (Ra), defined in JIS-B-0601, ranging from 3.0 to 4.5 µ m. As a material for the plastic sheet, there may be used those such as olefin resin, polyesters, polytetrafluoroethylene. It is preferred to use olefin resin such as polyethylene, polypropylene, polybutylene and the like from the economical or processing point of view. The wrapping pipe may be prepared for example by a method using the above device including the steps of: (a) drawing a plastic sheet from a plastic sheet roll; (b) cutting the sheet drawn by said rollers to a predetermined width; (c) rounding the sheet into a tubular form having an overlapping portion at opposing longitudinal sides thereof; (d) shaping the rounded sheet into a tubular form using a mold which is movably arranged around a core rod; (e) welding the overlapped portion of the sheet by ultrasonic waves to form a continuing pipe; (f) cutting the continuing pipe into a pipe with a predetermined length. The above and other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of a device for production of pipes for wrapping a bundle of hollow fibers; Fig. 2 is a perspective view illustrating a pipe shaping station in the device of Fig. 1; Fig. 3 is a section view of the pipe shaping station of Fig. 2; Fig. 4 is a perspective view of a wrapping pipe according to the present invention; Fig. 5 is a perspective view illustrating an example of a wrapping pipe of the prior art; and Fig. 6 is a perspective view illustrating another example of a wrapping pipe of the prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to Figs. 1 to 3, there is shown a device for manufacturing wrapping pipes for wrapping a bundle of hollow fibers according to the present invention, which comprises a sheet roll holding station 1, a sheet cutting station 2 for cutting a plastic sheet to a predetermined width, a sheet drawing station 3, a sheet rounding station 4 for guiding the sheet to the next station while rounding it into a cylindrical form overlapped at the opposite longitudinal sides of the sheet, a pipe shaping station 5 for welding the overlapped portion of the rounded sheet with ultrasonics to form a pipe, a pipe drawing station 6, a pipe cutting station 7 for cutting the pipe to a predetermined length, and a pipe ejecting station 8. These stations are arranged along the course of the plastic sheet. The sheet roll holding station 1 comprises a roll stand 11 and a sheet roller 12 which is rotatably mounted on the stand 11 and holds a roll 13 of plastic sheet S wound thereon. The plastic sheet S is drawn out from the sheet roll 13 by the sheet drawing station 3 and fed to the sheet cutting station 2 where the sheet is cut to a predetermined width. The width of the sheet S is determined on the basis of an inside diameter of the wrapping pipe to be produced so that it equals to the sum of a peripheral length of the pipe and an overlapping width of the opposing sides of the sheet S. The overlapping width of the sheet S is generally determined so as to have a length approximately equal to a width of the ultrasonic welding horn 59. The sheet cutting station 2 comprises a pair of cutters (not illustrated in the drawings) spaced each other to cut a plastic sheet S to a predetermined width. The sheet drawing station 3 includes a pair of rollers (3a, 3b) made of an elastomeric material such as natural rubber, synthetic rubber. The sheet S is then fed to the pipe forming station 10 including a sheet rounding station 4 and a pipe shaping station 5. The sheet rounding station 4 comprises a sheet guiding member 42 with a tapered groove 43, a rod supporting member 41 and a core rod 57. The core rod 57 is supported only at one end by the rod supporting member 41 and extends toward the pipe shaping station 5. The core rod 57 passes through the tapered groove 43, extends coaxially with a cavity or through-hole of the mold mentioned later, and terminates at a position apart from the outlet of the mold 51. The pipe shaping station 5 includes a mold 51, a forming rod 57, and a ultrasonic welding means 58. The mold 51 is divided into three parts, i.e., an upper left molding member 511, an upper right molding member 512 and a lower molding member 513 which are respectively grooved in their longitudinal direction to form a cylindrical cavity or through-hole 55 between them. The upper left molding member 511 is connected to an air cylinder 52 as shown in Fig. 2. Similarly, the upper right molding member 512 is connected to an air cylinder 53. The upper right and left molding members 511 and 512 are moved in the direction away from or close to the core rod 57 by the air cylinders 52 and 53 to open or close the mold. On the other hand, the lower molding member 513 is connected to an air cylinder 54 and moved up and down by the air cylinder 54. When producing the pipe, the upper right and left molding members 511 and 512 are moved inwardly or in the direction close to the core rod 57 by the air cylinders 52 and 53, while the lower molding member 513 is moved upwardly or in the direction close to the core rod 57 by the air cylinder 54. In the closed condition of the mold, however, the upper molding members 511 and 512 are arranged with a space between them to provide a long narrow cut or slit 56 for insertion of a welding horn 59 of the ultrasonic welding means 58. The welding horn 59 of the ultrasonic welding means 58 is tapered so as to have a width approximately equal to the width of the slit 56 between the upper right and left molding members 511 and 512. The lower end of the horn 59 has a rectangular cross section and is inserted into the slit 56 during operation. The pipe drawing station 6 is arranged next to the pipe forming station 10 and composed of a pair of rollers (not illustrated in the drawings). The rollers may be made of an elastomeric material such as natural rubber, synthetic rubber. The pipe cutting station 7 includes a cutting member so arranged as to cut the pipe in the direction perpendicular to the axis of the pipe. Under the rest of operation, the mold is opened and rested at their respective rest positions. The opening of the mold is carried out by moving the molding members 511, 512 and 513 in the respective directions indicated by arrows A, B and C in Fig. 3. At the initial stage, the plastic sheet S is drawn manually from the sheet roll 13 and inserted into spaces between the core rod 57 and molding members 511, 512 and 513 through the guiding groove 43 of the guiding member 42. During the course of these operations, the sheet S is rounded into a cylindrical form with an overlapped portion of the opposing longitudinal sides thereof. After completing the set of the sheet S, all the operations are automatically carried out as mentioned below. First, the mold 51 is closed by moving the molding members 511, 512 and 513 in the respective directions reverse to that of the arrows A, B and C in Fig. 3 until the molding members 511, 512 and 513 press the plastic sheet S against the core rod 57 as shown in Figs. 2 and 3. Then, the welding horn 59 of the ultrasonic welding means 58 is inserted into the slit 56 between the upper molding members 511 and 512 until it presses the overlapped portion of the sheet S against the surface of the core rod 57. The overlapped portion of the sheet S is welded to form a cylindrical portion or a pipe by ultrasonic waves put out from the welding horn 59. Since the inner side of the overlapped portion of the sheet S is pressed against the surface of the core rod 57 during ultrasonic welding, no difference in level is produced in the inner surface of the pipe produced. After the ultrasonic welding, the molding members 511, 512 and 513 are returned to the respective rest positions to open the mold 51. The welded cylindrical portion of the sheet S is then drawn by the pipe drawing station 6. At the same time, a new part of the sheet S is drawn from the sheet roll 1 and fed to the pipe forming station 10 as the rollers of the sheet drawing station 3 and the pipe drawing station 6 are driven under the conditions synchronized with each other. Then, the drawing operation of the sheet drawing station 3 and the pipe drawing station 6 are stopped. The welded cylindrical portion of the sheet S fed to the pipe ejecting station 8 is cut off at the pipe cutting station 7 to provide a wrapping pipe with a desired length and then taken out from the pipe ejecting station 8. Then, the molding members 511, 512 and 513 are moved inwardly to close the mold 51 again and the above sequential operations are repeated. During the sequential operations, the plastic sheet S fed from the sheet roll 1 is rounded into a cylindrical form so that opposing sides of the sheet are partially overlapped each other during passing through the sheet rounding station 4, and then formed into a pipe by welding the overlapped portion of the sheet with the ultrasonic welding means 58 during passing through the pipe shaping station 5. As will be understood from the above, according to the present invention the length and inside diameter of the pipe to be produced can be determined optionally by replacing the molding members and core rod and/or by adjusting the sheet cutting station and the pipe cutting station, thus making it possible to produce various kinds of wrapping pipes with a desired size. EXAMPLES Using the above device, there were produced pipes for wrapping a bundle of hollow fibers of an inside diameter of 30 mm and a length of 2000 mm with polypropylene sheets of a 0.3 mm thick, a 120 mm width and a center line mean roughness (Ra) shown in Table 1. The center line mean roughness (Ra) was measured with a contact type surface measuring system (Model TALY SURF-6, made by Rank Taylor Hobson Ltd.). A bundle of ten thousand hollow fibers with a diameter of 230 µ m was loaded into each of the resultant wrapping pipe to determine a rate of occurrence of fiber breakage or leakage. Results are shown in Table 1 along with the results for comparative specimens. In Table 1, the specimen with an asterisk indicates the wrapping pipe out of the scope of the present invention, and "SS" is an abbreviation for "supersonic". The comparative specimens were produced by extrusion molding with polypropylene so as to have an inside diameter of 30 mm and a length of 2000 mm. Table 1 shows the center line mean roughness (Ra) for each specimen, the measured surface roughness of the comparative specimens fell in the range of 1.6 to 3.0. No. Production Ra (µm) Breakage (%) leakage (%) Number of Samples 1 SS Welding 3.1 1.0 0 100 2 SS Welding 3.7 0 0.74 270 3 SS Welding 4.3 0.3 3.2 1000 4* SS Welding 5.2 0.2 2.0 1000 5* SS Welding 6.0 0.13 5.8 1500 6* Extrusion 2.0 2.37 1.1 3000 7* Extrusion 2.3 1.11 1.85 270 8* Extrusion 2.6 0.32 2.61 7500 9* Extrusion 2.7 0.7 8.8 1000 As will be seen from the results shown in Table 1, the rate of occurrence of fiber breakage increases with decrease in Ra, while the rate of occurrence of the leakage increases with increase in Ra. Further, it is preferred to use the wrapping pipes of which inner surface has the center line mean roughness (Ra) ranging from 3.0 to 4.5. The observation of the inner surfaces of the specimens Nos. 4 and 5 with an electron microscope showed that the high rate of occurrence of leakage results from sharp embossments of their inner surface. Accordingly, the present invention makes it possible to minimize the breakage and leaks of the hollow fibers during insertion into the wrapping pipes, which in turn makes it possible to improve the yield of the production of blood treatment devices. Further, it is possible to reduce the time required for readjustment or quality control of products, i.e., cylindrical containers loaded with a bundle of hollow fibers. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims.

Claims: A device of producing wrapping pipes for wrapping a bundle of hollow fibers from a plastic sheet, comprising: a pair of rollers for drawing a plastic sheet from a plastic sheet roll; a sheet cutting station (2) including a pair of cutters for cutting the sheet drawn by said rollers to a predetermined width; a cylindrical core rod (57) for rounding the sheet into a tubular form having an overlapped portion at opposing longitudinal sides thereof; a mold (51) movably arranged around said core rod (57) for shaping the rounded sheet into a tubular form, said mold having a through hole (55) and a slit (56) extending in the longitudinal direction of the mold, a ultrasonic welding means (58) including a welding horn (59) for welding the overlapped portion of the sheet by ultrasonic waves, said welding horn (59) being movably arranged above the slit (56) so that it is insertable into the slit to press the overlapped portion of the sheet against the core rod (57) to form a continuing pipe having an inner surface with no difference in level of the inner surface thereof; and a pipe cutting station (7) including a cutting member for cutting the continuing pipe into a pipe with a predetermined length. The device according to claim 1, wherein the mold is divided into an upper right molding member (511), an upper left molding member (512) and a lower molding member (513), each molding member being connected to an air cylinder for driving the molding member to form a cylindrical cavity or through-hole (55) between them. A method for the production of wrapping pipes using the device of claim 1 or 2 comprising the steps of: (a) drawing a plastic sheet from a plastic sheet roll; (b) cutting the sheet drawn by said rollers to a predetermined width; (c) rounding the sheet into a tubular form having an overlapped portion at opposing longitudinal sides thereof; (d) shaping the rounded sheet into a tubular form using a mold (51) which is movably arranged around a core rod (57); (e) welding the overlapped portion of the sheet by ultrasonic waves to form a continuing pipe; (f) cutting the continuing pipe into a pipe with a predetermined length.

Inventors: YONEDA ATSUSHI, YONEDA, ATSUSHI
Applicants: NIPRO CORP, NIPRO CORPORATION
Application year: 1994
Main classification: B29C53
IPC codes: B01D63, A61J3, B29C65, B29L23, B29C63, B01D65, B29C53